FILE - In this June 21, 2017, file photo, former FBI Director Robert Mueller, the special counsel probing Russian interference in the 2016 election, departs Capitol Hill following a closed door meeting in Washington. Mueller is using a grand jury in Washington as part of an investigation into potential coordination between the Trump campaign and Russia, according to a person familiar with the probe. The use of a grand jury, a standard prosecution tool in criminal investigations, suggests that Mueller and his team of investigators is likely to hear from witnesses and demand documents in the coming weeks. The person who confirmed to The Associated Press that Mueller had turned to a grand jury was not authorized to discuss the investigation by name and spoke on condition of anonymity. (AP Photo/Andrew Harnik, File)